군집의 분산을 이용한 수렴 검출 기능을 갖는 일반화된 MAP 등화기
A Generalized MAP Equalizer with Convergence Detection Using Cluster Variance
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초록
본 논문에서는 등화기 출력을 관찰하여 송신된 심벌을 추정시 그 사후 확률을 최대화하는 최대 사후 확률(MAP:Maximum A Posteriori probability) 기준 등화기를 M진 직교 진폭 변조(M-QAM: M-ary Quadrature Amplitude Modulation) 신호에 대해 일반화하고 계산 복잡성을 단순화하였다. 제안 방법에서는 M-QAM 시스템에서 I-채널과Q-채널을 분리하여 각각 추정하되 등화 초기에는 축소 신호점을 도입하고 정상 상태에서는 등화기 출력을 둘러싸는두 신호점을 사용하여 송신신호를 추정하였다. 결국 등화기 출력을 두 신호점 소스로부터 발생된 군집으로 모델링하였다. 아울러 제안방식은 초기 수렴속도와 정상 상태 성능을 개선하기 위해 두 동작 모드를 가지며 동작 모드는 군집의 분산값에 의해 선택된다. 또한 두 동작 모드는 신호 추정에 사용된 비선형 추정기의 파라미터를 조절하는 것으로간단히 구현되는 특징을 가진다. 모의실험을 통해 제안 방법이 16/64-QAM 신호에 대해 기존의 CMA 기반 블라인드등화 기법에 비해 개선된 수렴속도와 정상 상태 성능을 보이는 것을 확인하였다.
Abstract
In this paper, the Maximum A Posteriori probability (MAP) criterion equalizer that maximizes the posteriori probability of the transmitted symbol when estimating it from the equalizer output has been generalized to MQAM (M-ary Quadrature Amplitude modulation) signals and its computational complexity simplified. In the proposed method, for M-QAM systems, I-channel and Q-channel are estimated separately, but in the early stage of equalization the reduced constellations were introduced, and in the steady-state two signal points surrounding the equalizer output signal were used for estimating the transmitted symbols. Eventually equalizer output was modeled as clusters being generated from two signaling points source. The proposed method has two operating modes to improve the initial convergence speed and steady-state performance, the operating mode is selected by the variance of the clusters. In addition, the two operation modes are characterized by simple implementation by adjusting the parameters of the nonlinear estimator used to estimate the signal. Through simulation, the proposed method was confirmed to improve the convergence speed and steady-state performance compared to the existing CMA-based blind equalization technique for 16/64-QAM signals
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